Yilmaz Bayazit, Eph Sparrow and John Gorman
The purpose of this paper is to provide both directly applicable fluid-flow results and fluid-mechanic fundamentals for flow impinging at an angle of attack on a perforated plate.
Abstract
Purpose
The purpose of this paper is to provide both directly applicable fluid-flow results and fluid-mechanic fundamentals for flow impinging at an angle of attack on a perforated plate.
Design/methodology/approach
A physical situation was modeled with high fidelity, and the model was implemented by numerical simulation. The simulations spanned all possible flow regimes including laminar, intermittent (transitional) and turbulent, and the Reynolds numbers that defined each flow regime were definitively determined. The Reynolds numbers ranged from 0.1 to 30,000, the angles of attack included 0, 5, 15 and 22.5° and the host duct dimensions varied appropriately.
Findings
It was found that the perforated-plate pressure drop decreased moderately with an increasing angle of attack, an outcome directly relevant to design. The pattern of fluid flow caused by the presence of the plate was dominated by a large recirculation zone situated downstream of the plate in a corner between the plate and an adjacent wall. The recirculation zone played the role of a blockage which deflected the flow emerging from the apertures in the plate toward the opposite wall.
Originality/value
(a) Pressure drop information directly applicable to design, (b) downstream distance from the plate at which the plate-created flow disturbance disappears, (c) account taken of the intermittent flow regime between laminar and turbulent, (d) implementation of a new metric to characterize the strength of turbulence.
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Phillip Tanner, John Gorman and Eph Sparrow
The purpose of this study is to quantify the relationship between the fluid flow and pressure drop for perforated plates. The homogenization of non-uniform fluid flows is often…
Abstract
Purpose
The purpose of this study is to quantify the relationship between the fluid flow and pressure drop for perforated plates. The homogenization of non-uniform fluid flows is often accomplished by passing the fluid through perforated plates. The underlying principle for the accomplishment of flow homogenization is a tradeoff of pressure drop for flow uniformity.
Design/methodology/approach
The investigation, implemented by numerical simulation, is based on turbulent flow in pipes and across perforated plates. The approach is as follows: (a) to devise a model to determine pressure drop’s fluid flow information from a single-aperture, (b) to obtain this information for apertures of different shapes, (c) to determine this type of information for perforated plates situated in a circular pipe, (d) to compare the entire perforated-plate pressure drop with that for a single-aperture modular and (e) to analyze two identical perforated plates in series.
Findings
The pressure drop results for the single-aperture modular model agreed very well with those for a whole perforated plate in a round pipe, therefore negating the need to simulate the more complex situation. In addition to the parametric study with aperture shape and Reynolds number, porosities (20-60 per cent) and plate thicknesses were also varied. The results obtained here compared favorably with experimental data.
Originality/value
This work demonstrates an efficient method for analyzing and obtaining useful pressure drop information for perforated plates. For the first time, the porous media approach for modeling perforated plates is compared directly to complete, full-scale perforated plate applications and identical plates in series.
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John Gorman, Eph Sparrow and Kevin Krautbauer
The study described here aims to set forth an analysis approach for a specific biomedical therapeutic device principally involving fluid mechanics and resulting sound generation…
Abstract
Purpose
The study described here aims to set forth an analysis approach for a specific biomedical therapeutic device principally involving fluid mechanics and resulting sound generation. The function of the therapeutic device is to clear mucus from the airways of the lungs. Clearance of the airways is a primary means of relief for cystic fibrosis and is also effective in less profound dysfunctions such as asthma. The complete system consists of a device to periodically pulse air pressure and a vest that girdles the abdomen of the patient and receives and discharges the pulsating airflow. The source of pulsed air can be tuned both with respect to the amplitude and frequency of the pressure pulsations.
Design/methodology/approach
The key design tools used here are computational fluid dynamics and the theory of turbulence-based sound generation. The fluid flow inside of the device is multidimensional, unsteady and turbulent.
Findings
Results provided by the fluid mechanic study include the rates of fluid flow between the device and the inflatable vest, the rates of air supplied to and extracted from the device, the fluid velocity magnitudes and directions that result from the geometry of the device and the magnitude of the turbulence generated by the fluid motion and the rotating component of the device. Both the velocity magnitudes and the strength of the turbulence contribute to the quantitative evaluation of the sound generation.
Originality/value
A comprehensive literature search on this type of therapeutic device to clear mucus from the airways of the lungs revealed no previous analysis of the fluid flow and sound generation inside of the device producing the pulsed airflow. The results presented in this paper pinpoint the locations and causes of sound generation that can cause audible discomfort for patients.
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Abhimanyu Ghosh, Eph Sparrow and John Gorman
This paper aims to investigate and understand the fluid mechanics of piezometer rings, a device frequently encountered in engineering practice.
Abstract
Purpose
This paper aims to investigate and understand the fluid mechanics of piezometer rings, a device frequently encountered in engineering practice.
Design/methodology/approach
The investigation, implemented by numerical simulation, is based on turbulent flow in a pipe with a 90-degree bend. The pipe Reynolds numbers ranged from approximately 50,000 to 200,000. Two rings, with different dimensions, were investigated. Each ring consisted of four radially deployed straight segments of tubing which connect the pipe to a surrounding circular ring. The interconnections between the pipe and the ring were situated at 90-degree intervals around the circumference of the pipe.
Findings
The focus was directed to optimal circumferential locations of the radial connections, the optimal circumferential locations for accurate pressure measurements and the pressure drop penalty incurred by the use of a piezometer ring. For both of the investigated piezometer ring configurations, it was found that measurement locations situated just beyond the points of intermediate circumferential pressure variations were suitable for determining accurate values. The pressure drop was seen to increase because of the presence of the ring. For the smaller ring configuration, the increase in relative pressure drop was on the order 15 per cent, whereas the larger ring configuration lead to a 10 per cent increase.
Originality/value
This is the first attempt known to the authors to investigate and understand the fluid mechanics of piezometer rings.
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The purpose of this study is to examine the physical processes experienced by a particle-laden gas due to various types of collisions, different heat transfer modalities and jet…
Abstract
Purpose
The purpose of this study is to examine the physical processes experienced by a particle-laden gas due to various types of collisions, different heat transfer modalities and jet axis switching. Here, attention is focused on a particle-laden gas subjected to jet axis switching while experiencing fluid flow and heat transfer.
Design/methodology/approach
The methodology used to model and solve these complex problems is numerical simulation treated here as a two-phase turbulent flow in which the gas and the particles keep their separate identities. For the turbulent flow model, validation was achieved by comparisons with appropriate experimental data. The considered interactions between the fluid and the particles include one-way fluid–particle interactions, two-way fluid–particle interactions and particle–particle interactions.
Findings
For the fluid flow portion of the work, emphasis was placed on the particle collection efficiency and on independent variables that affect this quantity and the trajectories of the fluid and of the particles as they traverse the space between the jet orifice and the impingement plate. The extent of the effect depended on four factors: particle size, particle density, number of particles and the velocity of the fluid flow. The major effect on the heat transferred to the impingement plate occurred when direct heat transfer between the impinging particles and the plate was taken into account.
Originality/value
This paper deals with issues never before dealt with in the published literature: the effect of jet axis switching on the fluid mechanics of gas-particle flows without heat transfer and the effect of jet axis switching and the presence of particles on jet impingement heat transfer. The overall focus of the work is on the impact of jet axis switching on particle-laden fluid flow and heat transfer.
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In the last decade, Argentina has experienced a considerable decline in informal employment and wage dispersion. This paper extends a search model with exogenous human capital…
Abstract
In the last decade, Argentina has experienced a considerable decline in informal employment and wage dispersion. This paper extends a search model with exogenous human capital accumulation to include the informal sector. The model is parametrized to match Argentinian data between 1996 and 1998 – before the onset of the declining trend – and it is used to investigate the contribution of labor market measures to the falling informality, unemployment, and wage dispersion. The findings indicate that institutional factors did not contribute to the positive labor market trends observed; on the contrary, results show that higher severance pay and minimum wages increase informality and that the introduction of unemployment assistance contributed to the spread of informal contracts across the work force. Further, I find that compliance with minimum wage regulation strongly affects the final impact of these policies. While non perfect compliance might reduce unemployment, it reinforces the incentives of workers to move to the informal sector.